The invention relates to an automated apparatus and method for forming a hardfacing coating on a work piece with complex geometry and more particularly to an automated apparatus and method for deposition of a hardfacing layer on a roller cone of a drill bit.
Certain drill bits, also known as rock bits, are commonly used for drilling oil wells in petroleum applications and for drilling blast holes for blasting in mining applications. Various types of rock bits have been developed over the years. One type of rock bit is called a milled-tooth bit, which includes a bit body and one or more milled tooth cones. A typical milled-tooth bit with three milled-tooth cones is illustrated in FIG. 1.
A typical milled-tooth bit 10 includes three separate milled-tooth cones 12 which are attached to the bit body. Each cone 12 has a plurality of teeth protruding from the surface of the cone. The entire milled-tooth cone, including the teeth, typically is manufactured from a piece of steel. During operation, the bit is attached to a drill string (not shown) and the cones are in contact with an earthen formation. As the drill string rotates the bit, the three milled-tooth cones 12 also rotate around their respective axes.
Under normal drilling conditions, the relatively soft steel teeth of a milled-tooth cones are exposed to substantial abrasion and loading. This abrasion and loading can result in significant erosion and impact wear on the teeth. The wear on the teeth ultimately results in a reduction in the penetration rate of the drill bit and a shortened life of the drill bit.
A solution to the lack of wear resistance is to deposit a coating of wear-resistant material on the surfaces of the teeth. This process is sometimes referred to in the art as xe2x80x9chardfacing.xe2x80x9d Typical wear resistant material used in hardfacing includes tungsten carbide particles in a metal matrix. Deposition of the hardfacing material typically is accomplished using a manual welding process, such as oxyacetylene welding (OAW), atomic hydrogen welding, etc. In a manual process, a person holding a welding torch and a rod of hardfacing material will apply a coating of the hardfacing material to the surface of a tooth by welding. After one tooth has been coated, the person moves the torch, the hardfacing material, and/or the cone to permit the next tooth to be coated.
However, manual processes do not always produce satisfactory hardfacing coatings on milled teeth. Quality characteristics of a hardfacing coating are indicated, in part, by the thickness, uniformity, and coverage of the hardfacing coating on the tooth. The quality also is affected by the porosity of and the oxide and eta phase content in the coating. In a manual process, the consistency of these characteristics varies from operator to operator and even from time to time for the same operator. Sometimes the quality of a hardfacing coating may differ significantly from one tooth to another on the same cone.
An automated hardfacing system would provide a significant advantage by producing consistent quality characteristics during the hardfacing process. The improved quality of hardfacing of a cone may result in an increased penetration rate of the drill bit and ultimately lead to a longer drilling bit life. However, due to the complex geometry, inaccessibility to the faces of each tooth by a hardfacing torch, and the number of teeth on a milled-tooth cone, an automated hardfacing system for a rock bit has not been available because it is an enormous challenge to develop an automated hardfacing system capable of properly hardfacing some or all of the desired surfaces of each tooth.
For the foregoing reasons, there is an unfulfilled need in the art for an automated hardfacing system which is capable of producing consistent hardfacing coating on a work piece with complex geometry, such as a milled-tooth cone.
In one aspect, the invention relates to an apparatus for hardfacing a roller cone of a drill bit. The apparatus includes (1) a positioner having n axis (axes) of movement; (2) a holder having m axis (axes) of movement, wherein m+nxe2x89xa75; (3) a roller cone with a protruding tooth mounted on the holder; and (4) a controller which co-ordinates the movement of the positioner and the holder to deposit a hardfacing composition on an area of the roller cone. In some embodiments, the roller cone includes milled teeth or tungsten carbide inserts. In other embodiments, the roller cone includes a land or a groove on the cone surface, and the hardfacing composition is deposited on the land or the groove.
In another aspect, the invention relates to an apparatus for hardfacing a milled-tooth cone of a drill bit. The apparatus includes (1) a positioner having n axis (axes) of movement; (2) a holder having m axis (axes) of movement, wherein m+nxe2x89xa75; (3) a milled-tooth cone with a tooth mounted on the positioner; and (4) a controller which co-ordinates the movement of the positioner and the holder to deposit a hardfacing composition on the tooth of the milled-tooth cone. Alternatively, the milled-tooth cone may be mounted on the holder. In some embodiments, the apparatus may further include a hardfacing torch which is mounted either on the holder or on the positioner. In other embodiments, the controller may control a hardfacing torch travel speed, a hardfacing torch weave pattern, and a hardfacing torch stand-off distance from the milled-tooth cone. Furthermore, the controller may control a hardfacing composition, a hardfacing composition feed rate, an arc current, a voltage, and a gas flow rate. In some embodiments, the hardfacing composition is deposited on the tooth of the milled-tooth cone by a plasma transferred arc process, a pulsed plasma transferred arc process, a metal inert gas arc process, or a gas tungsten arc welding process. In other embodiments, the tooth may include a crest face, a leading face, a trailing face, an outside face, and an inside face, and the hardfacing composition may be deposited on the crest face and the leading face of the tooth. In other embodiments, the hardfacing composition may be deposited on the crest face, the leading face, the trailing face, the outside face, and the inside face of the tooth.
In one aspect, the invention relates to an apparatus for hardfacing a milled-tooth cone of a drill bit. The apparatus includes (1) a positioner holding a milled-tooth cone where the positioner has at least two axes of movement and the milled-tooth cone has a plurality of protruding steel teeth; (2) a robot holding a hardfacing torch where the robot has at least three axes of movement and the hardfacing torch is connected to a hardfacing composition including tungsten carbide and a metal matrix; (3) a robot controller which co-ordinates the movement of the positioner and the robot such that the hardfacing composition is deposited on the steel teeth of the milled-tooth cone by a pulsed plasma transferred arc process; and (4) a hardfacing torch controller which controls a hardfacing composition feed rate, a hardfacing torch travel speed, a hardfacing torch weave pattern, and a hardfacing torch stand-off distance from the milled-tooth cone.
In another aspect, the invention relates to an apparatus for hardfacing a roller cone of a drill bit. The apparatus includes (1) a roller cone having a protruding tooth; (2) means for holding the roller cone having m axis (axes) of movement; (3) means for holding a hardfacing torch having n axis (axes) of movement, wherein m+n greater than 5; (4) means for automatically controlling the movement of the roller cone and the hardfacing torch; and (5) means for depositing a hardfacing composition on the tooth of the roller cone.
In another aspect, the invention relates to a method for hardfacing a roller cone of a drill bit. The method includes (1) providing a roller cone having a protruding tooth and a hardfacing torch; (2) moving the roller cone by using a first apparatus having m axis (axes) of movement; (3) moving the hardfacing torch by using a second apparatus having n axis (axes) of movement, wherein m+nxe2x89xa725; and (4) depositing a hardfacing composition on the tooth of the roller cone with the hardfacing torch.
In yet another aspect, the invention relates to a method for hardfacing a milled-tooth cone of a drill bit. The method includes (1) providing a milled-tooth steel cone having a plurality of steel teeth where each steel tooth has at least one face; (2) providing a hardfacing torch having a tip; (3) moving the milled-tooth steel cone by a positioner; (4) moving the hardfacing torch tip to an area adjacent to the face of a steel tooth of the milled-tooth cone by a robot; (5) forming a plasma column between the hardfacing torch tip and the face of the steel tooth; (6) feeding a hardfacing composition into the plasma column; (7) pulsing an electrical current at a pulse rate to deposit a layer of the hardfacing composition on the face of the steel tooth; and (8) controlling the pulsing of the electrical current to minimize the formation of a weld pool on the face. The hardfacing composition is deposited on the steel teeth by coordinating the movement of the positioner and the holder.
In another aspect, the invention relates to a hardfaced roller cone manufactured by the following method. The method includes (1) providing a hardfacing torch and a roller cone having a protruding tooth; (2) moving the roller cone by using a positioner having m axis (axes) of movement; (3) moving the hardfacing torch by using a holder having n axis (axes) of movement, wherein m+nxe2x89xa75; and (4) depositing a hardfacing composition on the tooth of the roller cone with the hardfacing torch. In some embodiments, the tooth is formed of steel. In some embodiments, the hardfacing composition may include tungsten carbide and a metal matrix. The hardfacing composition may be deposited by a transferred plasma arc process, a pulsed transferred plasma arc process, a metal insert gas arc process, or a gas tungsten arc welding process.
In yet another aspect, the invention relates to a rock bit which includes a bit body having a leg and a hardfaced roller cone rotatably mounted on the leg. The hardfaced roller cone is manufactured by the following method: (1) providing a hardfacing torch and a roller cone having a protruding tooth; (2) moving the roller cone by using a positioner having m axis (axes) of movement; (3) moving the hardfacing torch by using a holder having n axis (axes) of movement, wherein m+nxe2x89xa75; and (4) depositing a hardfacing composition on the tooth of the roller cone with the hardfacing torch.